How do I render specific render layers using python?
Here's a little script, that iterates over all render layers and checks for some condition (e.g. does the layername start with 's'?). Then it disables all render layers and enables one that fulfills the condition until there are no more layers:

import bpy

render_layers = bpy.context.scene.render.layers

for layer in render_layers:

    # some condition
    if layer.name.startswith("s"):

        # disable all
        for l in render_layers:
            l.use = False

        # re-enable a single one that matched the condition
        layer.use = True

        # RENDER HERE